Generally, an LCD device is a display device for displaying a desired image by individually supplying a data signal according to image information to liquid crystal cells arranged in a matrix and controlling an optical transmittance of the liquid crystal cells.
In the LCD device, thin film transistor array substrates are formed on a large area mother glass, color filter substrates are formed on an additional mother substrate, and then the two substrates are attached to each other. Accordingly, liquid crystal panels are simultaneously formed thereby to enhance yield. A process for cutting the liquid crystal panels into each unit liquid crystal panel is used.
The process for cutting liquid crystal panels into each unit liquid crystal panel includes forming a groove of a certain depth on a surface of the mother substrate by using a cutting wheel, and cutting a liquid crystal panel by propagating a crack from the groove by external impact. The process for cutting liquid crystal panels into each unit liquid crystal panel will be explained in more detail with reference to the attached drawings.
FIG. 1 is an exemplary view schematically showing a planar structure of a unit liquid crystal panel having a thin film transistor array substrate and a color filter substrate attached to each other in an LCD device.
Referring to FIG. 1, a liquid crystal panel 10 comprises an image display portion 13 in which liquid crystal cells are arranged in a matrix, a gate pad portion 14 connected to gate lines of the image display portion 13, and a data pad portion 15 connected to data lines of the image display portion 13. The gate pad portion 14 and the data pad portion 15 are formed at an edge of the thin film transistor array substrate 1 that is not overlapped with the color filter substrate 2. The gate pad portion 14 supplies a scan signal supplied from a gate driver integrated circuit to the gate lines of the image display portion 13, and the data pad portion 15 supplies image information supplied from a data driver integrated circuit to the data lines of the image display portion 13.
Although not shown, on the thin film transistor array substrate 1 of the image display portion 13, the data lines to which image information is applied are arranged to be perpendicular to the gate lines to which a scan signal is applied. At each intersection between the data lines and the gate lines, a thin film transistor for switching liquid crystal cells, a pixel electrode connected to the thin film transistor for driving the liquid crystal cells, and a passivation layer formed on the entire surface of the thin film transistor array substrate for protecting the pixel electrode and the thin film transistor are provided. On the color filter substrate 2 of the image display portion 13, color filters deposited according to each cell region by a black matrix and a transparent common electrode corresponding to the pixel electrode formed on the thin film transistor array substrate 1 are provided.
The thin film transistor array substrate 1 and the color filter substrate 2 face each other with a cell gap, and are attached to each other by a sealant formed at an outer periphery of the image display portion 13. Also, a liquid crystal layer (not shown) is formed in the cell gap between the thin film transistor array substrate 1 and the color filter substrate 2.
FIG. 2 is an exemplary view showing a sectional structure of liquid crystal panels formed by attaching a first mother substrate 20 on which the thin film transistor array substrates 1 are formed to a second mother substrate 30 on which the color filter substrates 2 are formed.
Referring to FIG. 2, the unit liquid crystal panels are formed so that one side of each thin film transistor array substrate 1 is protruded longer than that of each color filter substrate 2. The reason is because the gate pad portion 14 and the data pad portion are formed at the edge of each thin film transistor array substrate 1 that is not overlapped with the color filter substrate 2.
Accordingly, the color filter substrates 2 formed on the second mother substrate 30 are spaced from each other by a dummy region 31, which corresponds to an area in which the thin film transistor array substrate 1 formed on the first mother substrate is protruded longer than the color filter substrate 2. Each unit liquid crystal panel is properly arranged to utilize the first mother substrate 20 and the second mother substrate 30 to the maximum. Generally, the unit liquid crystal panels are spaced from each other by a dummy region 32, and a dummy region 21 for a processing margin is formed at the edge of the first and second mother substrates 20 and 30.
After attaching the first mother substrate 20 where the thin film transistor array substrates 1 are formed to the second mother substrate 30 where the color filter substrates 2 are formed, liquid crystal panels are individually cut. At this time, the dummy region 31 for separating the color filter substrates 2 of the second mother substrate 30 from each other, the dummy region 32 for separating the unit liquid crystal panels from each other, and the dummy region 21 formed at the edge of the first and second mother substrates 20 and 30 are simultaneously removed.
FIGS. 3A and 3B are exemplary views showing one embodiment of a cutting wheel used to cut a liquid crystal panel. As shown, a disc-shaped cutting wheel 40 is provided with a through hole 41 for accommodating a support spindle (not shown) at the center thereof, and sharp blades 42 are formed along the edge of the cutting wheel 40.
The cutting wheel 40 is adhered to a glass liquid crystal panel with a certain pressure and rotates thereby to form a groove of a certain depth. Then, the liquid crystal panel is cut by propagating a crack downward by external impact.
However, the conventional cutting wheel 40 may form an undesired groove on the liquid crystal panel since it is susceptible to slide on the liquid crystal panel. Also, it is impossible to precisely control the propagation direction of the crack from the groove formed on the liquid crystal panel. Additionally, high pressure of the cutting wheel 40 on the liquid crystal panel is required, and the quality of the cut surface of the liquid crystal panel may be deteriorated due to the large contact surface between the cutting wheel and the liquid crystal panel.